Crash when using an invalid regular expression

[jonathanhefner]

Issue for discussion thread https://groups.google.com/d/topic/elm-discuss/7Uwl5-usqjs/discussion

Basically, JavaScript's RegExp (which is what Elm's Regex sits on top of) can throw an exception when given an invalid string. Examples:

RegExp("a"); // OK
RegExp("\\"); // Exception!
RegExp("("); // Exception!
RegExp("(?"); // Exception!
RegExp("(?:"); // Exception!
RegExp("?"); // Exception!
RegExp("+"); // Exception!
RegExp("*"); // Exception!

The obvious fix is to make Elm's Regex.regex return a Result (or a Maybe), but that seems like a pain to work with. It's also an API-breaking change, which I have no problems with whatsoever, but others might.

The only other solution I can think of is to escape characters at the end of an input string until no exception is thrown. For example:

RegExp("(?:"); // Exception!
RegExp("(?\\:"); // Exception!
RegExp("(\\?\\:"); // Exception!
RegExp("\\(\\?\\:"); // OK

It's a bit hacky though, and may not follow the principle of least surprise. Thoughts?

[Dobiasd]

In my opinion the API-breaking change is the better solution. I prefer Result over Maybe, since the exceptions message can be seen then.

[rudolf-adamkovic]

+1 for API-breaking changes. The best thing about Elm is that it's opinionated.

[rtfeldman]

Duplicate of #378, which has further discussion.

[jvoigtlaender]

Okay, closing this here as a duplicate.